He was so bloody light on his feet in human form and paws in animagus form, so even though her ears were perked, when he pounced on her tail, she was taken by surprise, jumping so that all four of her own paws lifted from the ground at once. When she came back down, she swatted playing fully at him, turning her body so that her tail tugged free from his paws.
And then, Astoria turned, darting down the bank of the creek a ways until she found a spot where the water was moving a little faster, the creek a little wider, with just a few rocks jutting out into makeshift stepping stones. With a certain amount of speed and grace, she hopped from the bank to the first rock, moving to each subsequent one with agility until she was able to hop onto the other bank. She didn't even bother to look back at him, instead just taking off, knowing he would be close behind.